Laser system

Abstract

A laser system comprising: a laser operable to generate a laser beam; an optical system comprising a first optical element and a second optical element; and an output through which the laser beam exits the laser system; the laser, optical system and output arranged such that the laser beam travels to the first optical element, the second optical element and the output sequentially; wherein the first optical element has a first focal length, the second optical element has a second focal length equal to the first focal length, and the second optical element is spaced from the first optical element by a distance of two times the first focal length.

1 . A laser system comprising:
 a laser operable to generate a laser beam;   an optical system comprising a first optical element and a second optical element; and   an output through which the laser beam exits the laser system;   the laser, optical system and output arranged such that the laser beam propagates to the first optical element, the second optical element and the output sequentially;   wherein the first optical element has a first focal length, the second optical element has a second focal length equal to the first focal length, and the second optical element is spaced from the first optical element by a distance of two times the first focal length.   
     
     
         2 . The laser system of  claim 1 , wherein the laser comprises an excimer laser. 
     
     
         3 . The laser system of  claim 2 , further comprising a pulse stretcher for increasing a pulse length of a pulse in the laser beam. 
     
     
         4 . The laser system of  claim 3  wherein the pulse stretcher is arranged between the laser and the first optical element. 
     
     
         5 . The laser system of  claim 4 , wherein the pulse stretcher comprises a pulse stretcher output through which a pulse of increased pulse length may exit the pulse stretcher, and wherein the first optical element is located proximal to the pulse stretcher output. 
     
     
         6 . The laser system of  claim 1 , further comprising a pulse stretcher for increasing a pulse length of a pulse in the laser beam. 
     
     
         7 . The laser system of  claim 6 , wherein the pulse stretcher is arranged between the laser and the first optical element. 
     
     
         8 . The laser system of  claim 7 , wherein the pulse stretcher comprises a pulse stretcher output through which a pulse of increased pulse length may exit the pulse stretcher, and wherein the first optical element is located proximal to the pulse stretcher output. 
     
     
         9 . The laser system of  claim 8  wherein a distance between the pulse stretcher output and the first optical element is less than the first focal length. 
     
     
         10 . The laser system of  claim 1 , wherein the second optical element receives the laser beam directly from the first optical element. 
     
     
         11 . The laser system of  claim 1 , further comprising a housing within which the laser and the optical system are disposed, wherein:
 the housing has an exit aperture at or proximal to the output of the laser system; and   the second optical element is located proximal to the exit aperture.   
     
     
         12 . The laser system of  claim 11 , wherein the distance between the exit aperture and the second optical element is less than the first focal length. 
     
     
         13 . The laser system of  claim 1 , further comprising:
 a second optical system comprising a third optical element and a fourth optical element;   wherein the third optical element has a third focal length, the fourth optical element has a fourth focal length equal to the third focal length, and the fourth optical element is spaced from the third optical element along the optical axis by a distance of two times the third focal length.   
     
     
         14 . The laser system of  claim 8 , further comprising a second pulse stretcher. 
     
     
         15 . A lithographic apparatus comprising:
 a laser system comprising:
 a laser operable to generate a laser beam; 
 an optical system comprising a first optical element and a second optical element; and 
 an output through which the laser beam exits the laser system; 
 the laser, optical system and output arranged such that the laser beam propagates to the first optical element, the second optical element and the output sequentially; 
 wherein the first optical element has a first focal length, the second optical element has a second focal length equal to the first focal length, and the second optical element is spaced from the first optical element by a distance of two times the first focal length. 
   
     
     
         16 . The lithographic apparatus of  claim 15 , further comprising a pulse stretcher for increasing a pulse length of a pulse in the laser beam, wherein
 the pulse stretcher is arranged between the laser and the first optical element and the pulse stretcher comprises a pulse stretcher output through which a pulse of increased pulse length may exit the pulse stretcher, and wherein the first optical element is located proximal to the pulse stretcher output.   
     
     
         17 . The lithographic apparatus of  claim 15 , further comprising a housing within which the laser and the optical system are disposed, wherein:
 the housing has an exit aperture at or proximal to the output of the laser system; and   the second optical element is located proximal to the exit aperture.   
     
     
         18 . The lithographic apparatus of  claim 17 , wherein the distance between the exit aperture and the second optical element is less than the first focal length. 
     
     
         19 . A laser system comprising:
 a laser operable to generate a laser beam;   an optical system comprising a first optical element and a second optical element; and   an output through which the laser beam exits the laser system;   the laser, optical system and output arranged such that the laser beam propagates to the first optical element, the second optical element and the output sequentially;   wherein the first optical element has a first focal length, the second optical element has a second focal length, and the second optical element is spaced from the first optical element by a distance substantially equal to the sum of the first focal length and the second focal length.